Thanks Orson - it's weird and yup, Project 64 followed by Music tool ad leaving a bit of time before ticking music mod.
I really do appreciate the help, sorry it's a pain in the arse
EDIT: Reinstalled music tool, done the offset check, still the same. The loading roster on the tool and code is showing 0x5260. Ah well - as you say I can play the game! I'll try a full reinstall tomorrow as I think I have it in my head now